1. Field of the Invention
The present invention relates to an image forming apparatus including an image reading mechanism that reads an image of a document and an image inspection mechanism that reads a printed image, in which in the image inspection mechanism, the printed image and the image of the document are compared, and thus a printing state is inspected.
2. Discussion of the Background
In conventional image forming apparatuses, a quality of a printed image varies over time or when the change in an environment such as temperature and humidity occurs. Thus, to prevent such a variation of the image quality, conventionally, a sensor has been provided, for example, that measures a toner density in a recording sheet after the printing. In the image forming apparatus with the sensor, for example, a toner discharge amount in a transfer unit is controlled based on the toner density measured by the sensor, and information obtained by the sensor is fed back to optimize the image forming process.
In recent years, due to a demand for high reproducibility of an image after the printing, image forming apparatuses including an image inspection mechanism have started to become popular. The image is again read from the printed recording sheet in the image inspection mechanism, and thus the printing state is inspected. As an example of the image forming apparatus including the image inspection mechanism, a printer connected to a print server through a network has been proposed (see Japanese Unexamined Patent Application Publication No. 2006-082398). The printer disclosed in Japanese Unexamined Patent Application Publication No. 2006-082398 prints on a recording sheet, an image based on document image data received from the print server through the network, and then reads the printed recording sheet with a line sensor (solid-state image sensing device). Then, a determination unit compares an inspection image data obtained by the line sensor with the document image data, and thus the printing state of the printer is inspected.
In the conventional image forming apparatuses provided with the image inspection mechanism including the printer disclosed in Japanese Unexamined Patent Application Publication No. 2006-082398, an optical system component in the image inspection mechanism is not configured to have a spectral characteristic that is the same as that of an optical system component for acquiring image data from a document image. Specifically, the printer disclosed in Japanese Unexamined Patent Application Publication No. 2006-082398 prints the document image data transmitted from the print server. Thus, the spectral characteristic of an optical system device used for generating document image data as a print target needs to be estimated, and the characteristics of any optical system components are difficult to optimize.
The image inspection mechanism includes, as optical system components, a light source for light radiated on a document as an image reading target, a solid-state image sensing device that converts reflected light from the document into an electrical signal, and an image forming optical system that forms an image in the solid-state image sensing device from the reflected light from the document. The spectral characteristics of the image inspection mechanism are determined by the spectral characteristics of an optical member including the light source and the image forming optical system and of the solid-state image sensing device. If the spectral characteristic of the optical system component is different between the image reading mechanism and the image inspection mechanism, a large difference in tint is produced between the inspection image data read by the image inspection mechanism and the document image data. Thus, a stable image quality cannot be obtained.
In the conventional image forming apparatus including the image reading mechanism and the image inspection mechanism, an image reading speed and an image reading width need to be different between the image reading mechanism and the image inspection mechanism to downsize the apparatus and achieve a low manufacturing cost. Due to the difference between the image reading mechanism and the image inspection mechanism in the spectral characteristics, reading speeds, and reading widths, an appropriate exposure amount for image reading cannot be obtained in the image inspection mechanism. If the reading speed of the image inspection mechanism is slow, the exposure amount from the light source is too large, thereby causing overexposure (saturation) in the image data. If the reading speed of the image inspection mechanism is fast, the exposure amount from the light source is insufficient, thereby causing noise such as underexposure in the image data. As described above, in the conventional image forming apparatus, the difference between the image reading mechanism and the image inspection mechanism in apparatus features has been a cause of deteriorating the accuracy of image forming process optimization based on the inspection on the printed image in the image inspection mechanism.